Nanomachining, by definition, involves mechanically removing nanometer-scaled volumes of material from, for example, a photolithography mask, a semiconductor substrate/wafer, or some other monolith. For the purposes of this discussion, “substrate” will refer to any object upon which nanomachining may be performed.
Typically, nanomachining is performed by applying forces to a surface of a substrate with a tip (e.g., a diamond cutting bit) that is positioned on a cantilever arm of an atomic force microscope (AFM). More specifically, the tip is typically first inserted into the surface of the substrate. Then, the tip is dragged through the substrate in a plane that is parallel to the surface (i.e., the xy-plane). This results in displacement and/or removal of material from the substrate as the tip is dragged along. However, this nanomachining process also results in the tip being subjected to a substantial amount of lateral stress as the tip is moved laterally in the xy-plane to displace substrate material.
One application of nanomachining involves the subtractive defect repair of photomasks. In other words, one application of nanomachining involves removing defects that form in photomasks either during the manufacturing thereof or as the masks are used over and over during photolithography. According this application, the tip is again dragged laterally, this time through the material that constitutes a defect, and is again subjected to a substantial amount of lateral stress.
As photomask and electronic device feature sizes have continued to decrease with the continued advancement of semiconductor technology, the AFM tips used for nanomachining have become high aspect ratio (HAR) tips. For example, tips currently used typically have aspect ratios of 1.3 or higher. Unfortunately, HAR tips have exhibited a propensity for deflection under traditional nanomachining methods. Thus, these tips have become more and more unsuitable for nanomachining of extremely small features, particularly those features where vertical edges are desired. These tips have also proven to be more and more unsuitable for the removal of extremely small defects buried deep in a mask or other substrate, as deflection of the tip reduces the ultimate feature-size resolution of the nanomachining process.